When turbine-powered aircraft land, the wheel brakes and the imposed aerodynamic drag loads (e.g., flaps, spoilers, etc.) of the aircraft may not be sufficient to achieve the desired stopping distance. Thus, the engines on most turbine-powered aircraft include thrust reversers. Thrust reversers enhance the stopping power of the aircraft by redirecting the engine exhaust airflow, via various moveable thrust reverser components, in order to generate reverse thrust. When stowed, the moveable thrust reverser components typically form a portion of the engine nacelle and forward thrust nozzle. When deployed, the moveable thrust reverser components typically redirect at least a portion of the airflow (from the fan and/or engine exhaust) forward and radially outward, to help decelerate the aircraft.
Various thrust reverser designs are commonly known, and the particular design utilized depends, at least in part, on the engine manufacturer, the engine configuration, and the propulsion technology being used. Thrust reverser designs used most prominently with turbofan engines fall into two general categories: (1) fan flow thrust reversers, and (2) mixed flow thrust reversers. Fan flow thrust reversers affect only the bypass airflow discharged from the engine fan. Whereas, mixed flow thrust reversers affect both the fan airflow and the airflow discharged from the engine core (core airflow).
Fan flow thrust reversers are typically used on relatively high-bypass ratio turbofan engines. Fan flow thrust reversers include so-called “Cascade-type” or “Translating Cowl-type” thrust reversers. Fan flow thrust reversers are generally positioned circumferentially around the engine core aft of the engine fan and, when deployed, redirect fan bypass airflow through a plurality of cascade vanes disposed within an aperture of a reverse flow path. Typically, the moveable thrust reverser components of a fan flow thrust reverser designs include one or more translating sleeves or cowls (“transcowls”) that, when deployed, open an aperture, expose cascade vanes, and create a reverse flow path. Fan flow reversers may also include so-called pivot doors or blocker doors which, when deployed, rotate to block the forward thrust flow path.
In contrast, mixed flow thrust reversers are typically used with relatively low-bypass ratio turbofan engines. Mixed flow thrust reversers typically include so-called “Target-type,” “Bucket-type,” and “Clamshell Door-type” thrust reversers. The moveable thrust reverser components of these types of thrust reversers typically include two or more pivoting doors that rotate, simultaneously opening a reverse flow path through an aperture and blocking the forward thrust flow path. However, a transcowl type thrust reverser could also be configured for use in a mixed flow application. Regardless of type, mixed flow thrust reversers are necessarily located aft or downstream of the engine fan and core, and often form the aft part of the engine nacelle.
The moveable thrust reverser components in each of the above-described designs are moved between the stowed and deployed positions by a thrust reverser actuation control system. The thrust reverser actuation control system may include a power drive unit (PDU), which selectively supplies a drive torque. A drive train that includes one or more drive mechanisms, such as flexible rotating shafts, may interconnect the PDU to a plurality of actuators to transmit the PDU's drive torque to the actuators, which are coupled to the moveable thrust reverser components.
The PDU in many thrust reverser actuation control systems is being implemented using an electric motor. As may be appreciated, a thrust reverser PDU, when deploying the thrust reverser movable components, preferably accelerates the actuators and associated movable components as quickly as possible, and then very quickly brings the actuators and movable components to a stop. Near the end of a deploy operation, the aerodynamic load typically becomes an overhauling load, which would tend to accelerate the actuators and the electric motor. Thus, near the end of a deploy operation, the electric motor is typically configured as an electromagnetic brake to slow the actuators down.
When electrical braking of an electric machine, such as the electric motor in a thrust reverser actuation system, is required and electrical power cannot be directed back to the power source, a parasitic load resistor (PLR) or aiding load resistor (ALR) is generally provided. The PLR or ALR, which may be passively or actively controlled, is an undesirable heat source that is typically located in the thrust reverser actuation control system controller. The PLR or ALR also undesirably increases system weight.
Hence, there is a need for a system and method of dissipating electric power during electric motor braking in a thrust reverser control system, while simultaneously reducing the weight of the thrust reverser control system and simplifying the electronic controls. The present invention addresses one or more of these needs.